1. Field of the Invention
The present invention relates to an image forming system, such as a copying machine, a printer, and a facsimile machine, achieving double-sided image formation on a sheet of recording material.
The invention also relates to an image forming system, such as a copying machine, a printer, and a facsimile machine, allowing the selection of the facing direction of a sheet of recording material to be discharged and achieving-double-sided image formation on a sheet of recording material.
2. Description of the Related Art
Recently, there has been an increasing need for an image forming apparatus capable of recording images on both the main and back sides of a sheet of recording material. The image forming apparatus of this type is arranged in such a manner that a sheet of recording material bearing an image on one side is reversed through a switch back mechanism or the like and fed again to an image forming section, thereby allowing an image to be formed also on the back side.
The foregoing arrangement is achieved by, for example, arranging in such a manner that a space used for switch back is formed in the main body or a peripheral apparatus to be retrofitted, or a space used for switch back is provided in an outside space of the image forming apparatus and part of a sheet of recording material is thereby exposed temporarily to the outside of the apparatus.
To be more specific, Japanese Unexamined Patent Publication JP-A 1-281249 discloses an arrangement providing a switch back path in a sheet treatment apparatus attached to one side portion of the main body of the image forming apparatus. Also, Japanese Unexamined Patent Publication JP-A 2-255476 proposes an arrangement of a switch back unit that temporarily exposes part of a sheet to the outside of the apparatus using a normal/reverse rotating roller.
A problem in the case of providing the space used for switch back in the main body of the image forming apparatus or the peripheral apparatus to be retrofitted is that the main body apparatus or the peripheral apparatus inevitably increases in size and the interior arrangement becomes more complicated, which results in the higher costs.
Also, a problem in the case of utilizing an outside space as the space used for switch back is that an object present within the space portion causes a trouble when a sheet of recording material is switched back, which limits the surrounding circumstances where the image forming apparatus is installed.
Further, in a case where the outside space is provided above a paper discharge tray, there arises a problem that when a post-treatment apparatus is retrofitted to a discharge section, the post-treatment apparatus is limited to those having a specific structure adapted for switch back.
Meanwhile, in the field of an image forming apparatus, besides an apparatus furnished solely with a copying function, a printing function, or an image data transmitting function, a multi-functional image forming system furnished with these functions has made its appearance in recent years. In regard to the multi-functional image forming system, there has been an increasing need for an image forming apparatus capable of outputting a sheet of recording material bearing an image either face up or face down, and recording images on both the main and back sides of a sheet of recording material.
The image forming system of this type is generally arranged in such a manner that a space used for switch back is provided in the main body or a peripheral apparatus to be retrofitted, or an outside space of the image forming apparatus is utilized as a space used for switch back and part of a sheet of recording material is thereby exposed temporarily to the outside, according to which a sheet of recording material bearing an image on one side is reversed through a switch back mechanism or the like, or transported to a paper discharge tray or a post-treatment apparatus without being reversed, or the reversed sheet of recording material is fed again to the image forming section, thereby allowing an image to be formed also on the back side.
In the case of changing the facing direction of a sheet of recording material to be discharged or forming images on both the main and back sides by switching back the sheet of recording material, the reversing mechanism for switching back a sheet of recording material becomes complicated or more than one reversing mechanism is needed.
For this reason, when all the reversing mechanisms for switching back a sheet of recording material are provided in the main body of the image forming apparatus or a peripheral apparatus to be retrofitted, there arises a problem that the main body apparatus or the peripheral apparatus increases in size and becomes more complicated, which results in the higher costs.
Also, as with the aforementioned case, in a case where a single reversing mechanism is provided and an outside space is utilized as a space used for switch back, an object present within a portion utilized as the space used for switch back causes a trouble when a sheet of recording material is switched back, which limits the surrounding circumstances where the image forming apparatus is installed.
Further, as with the aforementioned case, in a case where the outside space is provided above a paper discharge tray, there arises a problem that when a post-treatment apparatus is retrofitted to a discharge section, the post-treatment apparatus is limited to a specific post-treatment apparatus adapted for switch back.